They why did Finland cede territory to the Soviet Union?
Finland was eventually defeated in early 1940 by a massive Soviet commitment of troops and equipment. Their casualties were tremendous, but they won. They imposed their territorial terms on Finland and then went and licked their wounds as they lost large numbers of troops in the war (in the range of 100 to 200 thousand). In 1941, the Finns joined the Germans in operation Barbarossa and retook the seized areas and then some. After fighting for three years the Finns were once again crushed by Soviet forces and they sued for peace. The Soviets took more land in the peace settlement, shaping the current borders.